Closure structure for silo unloader collector arm



1967 F. E. BUSCHBOM 3,301,412

CLOSURE" STRUCTURE FOR SILO UNLOADER COLLECTOR ARM Original Filed May22, 1965 5 Sheets-Sheet 1 D *7 1 L J T l r 80 I g7 I W l9 x 39 55 Q I 84I I 7 1 86 an as 1s 15 42 43 62 INVENTOR. fiomfifiuscflsom Mafia I'dA-rroAwEYJ CLOSURE STRUCTURE FOR SILO UNLOADER COLLECTOR ARM 5Sheets-Sheet 2 Original F iled May 22.

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CLOSURE STRUCTURE FOR SILO UNLOADER COLLECTOR ARM Original Filed May 22,1963 5 Sheets$heefc 5 INVENTOR. FLomf. Bl/J'CHBOM A'rraR/vsYJ 3 1967 F.E. BUSCHBOM 3,301,412

' CLOSURE STRUCTURE FOR $11.10 UNLOADER COLLECTOR ARM Original Filed May22, 1963 5 Sheets-Sheet 4 Fl 6. 6 INVENTOR.

FL 0 YD 1f. 50561180114 BY B/zaddoo'fiund Arron/vans Jan. 31, 1967 F. E.BUSCHBOM 3,301,412

CLOSURE STRUCTURE FOR SILO UNLOADER COLLECTOR ARM Original Filed May 22.1963 5 SheetsSheet 5 INVENTOR.

FL am 5. BU-SCHBOM Ma aw HTTORNEYJ United States Patent 3,301,412CLOSURE STRUCTURE FOR 8110 UNLOADER COLLECTOR ARM Floyd E. Buschborn,Long Lake, Minn., assignor to Vandale Corporation, Long Lake, Minn., acorporation of Minnesota Application May 22, 1963, Ser. No. 282,475,which is a division of application Ser. No. 27,435, May 6, 1960, nowPatent No. 3,232,456, dated Feb. 1, 1966. Divided and this applicationMar. 11, 1965, Ser. No.

6 Claims. (Cl. 214-17 This application is a division of Serial No.282,475 filed May 22, 1963, now Patent No. 3,232,456. Serial No. 282,475is a division of Serial No. 27,435, filed May 6, 1960, now abandoned,for Unloader.

This invention relates to new and useful improvements in unloaders forsilos or the like, as exemplified by top surface unloaders such as shownin Van Dusen Patent 2,719,058, and Buschbom Patents 2,794,560 and2,877,- 907.

While great strides have been made in the silo unloader art and anunloader for positioning on the top surface of ensilage within a towersilo and for unloading the ensilage from such silo has now becomefeasible, as shown in the foregoing patents, numerous problems haveremained, and improvements have been sought. It is to some of theseproblems that this invention is directed.

A general object of this invention is to provide a silo unloader havingnew and improved features.

A further object of this invention is to provide new and useful closurestructure for the collector arm of a silo unloader, providingsubstantial safety for :the operator and precluding inadvertentengagement of the collector arm mechanism with extraneous objects.

A further object of this invention resides in new and useful structurefor joining the torque arm of a silo unloader to the unloader frame.

A further object of this invention resides in the utilization of new andimproved collector arm closure structure serving as means for supportingan adjustably positioned counterweight.

A further object of this invention resides in a counterweight slide fora silo unloader collector arm forming a portion of the collector arm andclosure means.

Still a further object of this invention resides in the cooperation ofthe collector arm and closure means with the center impeller housing ofa silo unloader.

Still a further object of this invention resides in the specificcollector arm structure and its cooperation with the central impellerfor efficient feeding of :the ensilage into the central impeller.

Still a further object of this invention resides in the provision of thecollector arm having new and unique flighting arrangement forcooperation with the silo unloader impeller housing.

Still a further object of this invention resides in new and usefulstructural improvements in the central impeller structure for providingmore efiicient material flow.

Yet a further object of this invention resides in the specific structureof the new and useful central impeller rotor.

Yet a further object of this invention resides in the specificconfiguration of the central impeller housing.

Yet a further object of this invention resides in the new and usefulguide structure of the invention whereby horizontal positioning of theguide means adjacent the silo wall is provided.

Another object of this invention resides in the structural details ofthe silo unloader support tripod means.

-'A still further object of this invention resides in the accessibilityof the adjusting structure for determining the longitudinal position ofthe guide wheels relative to the collector arm.

Other and further objects of the invention are those inherent andapparent in the structure as described, pictured and claimed.

To the accomplishment of the foregoing and related ends, this inventionthen comprises the features hereinafter fully described and particularlypointed out in the claims, the following description setting forth indetail certain illustrative embodiments of the invention, these beingindicative, however, of but a few of the various ways in which theprinciples of the invention may be employed.

The invention will be described with reference to the drawings in whichcorresponding numerals refer to corresponding parts and in which:

FIGURE 1 is a top plan view of the silo unloader of this invention inposition on the top surface of ensilage within a tower silo (shown inhorizontal section);

FIGURE 2 is an enlarged fragmentary plan view of the collector armstructure of FIGURE 1;

FIGURE 3 is a partial fragmentary plan, partial phantom viewillustrating cooperation of the collector arm auger flighting structurewith the central impeller;

FIGURE 4 is a vertical sectional view on an enlarged scale, taken alongthe line and in the direction of the arrows 44 of FIGURE 2;

FIGURE 5 is a vertical sectional view taken along the line and in thedirection of the arrows 5-5 of FIG- URE 4;

FIGURE 6 is a fragmentary enlarged elevational view, partially brokenaway, of the end of the collector arm adjacent the silo wall;

FIGURE 7 is a fragmentary elevational view showing the guide wheelstructure of the instant invention;

FIGURE 8 is an enlarged fragmentary plan view showing the means by whichthe torque arm is connected to the silo unloader support triangle; and

FIGURE 9 is a fragmentary elevational view taken along the line and inthe direction of the arrows 9-9 of FIGURE 8.

Reference is now made to :the drawings, and specifically to FIGURE 1,for the following description. In FIG- URE 1 there is shown theconfining wall 10 of a conventional tower silo, the wall 10 beingconstructed of concrete staves, wood or other appropriate material. Thewall 10 is usually only of more or less circular configuration, sincesilos are usually out-of-round. As is well known, :the silo is providedwith a plurality of vertically aligned apertures, open down to the levelof the ensilage and closed below that point. The aligned verticalapertures are separated by cross bars one of which is shown at 11 inFIGURE 1. The silo and unloader cooperate in the manner described inPatents 2,719,058, 2,794,560 and 2,877,907 and reference is made theretofor more specific details of such background cooperation.

The silo unloader generally designated 12 is shown in plan in FIGURE 1,and includes a guide arm assembly generally designated 13, a torque armassembly generally designated 14, a chute generally designated 15, acollector arm generally designated 16, a drive hub assembly generallydesignated 17, a suspension ring assembly 18, and gear box assembly 19,motor 20, drive structure 21 and frame 22.

Guide arm assembly 13 includes a wheel 23 journalled about a verticalaxis, and a wheel 24 journaled about a horizontal axis, all perhaps bestshown in FIGURE 7. Wheel 23 is journalled on a guide arm extension 25which is in the form of a rod having an outside diameter slightlysmaller than the inside diameter of guide arm 26, which is a sleeve orpipe, so that extension 25 may be inserted therein and extended orretracted for adjustment (moved leftwardly or rightwardly with referenceto FIGURE 7). When proper adjustment is secured, it is secured fixedlytherein by set screw 27 or other suitable means.

Arm 26 is flattened at end 28 and bolted to the strap member 29extending between and secured by lugs to frame members 30 and 31. Thisis best shown in FIG- URES 1, 2 and 7.

Wheel 24 is journalled to a guide arm support rod 32 received in a shortsleeve 33 welded or otherwise secured to the advance side of the arm 26.It may be moved upwardly or downwardly therein, since the externaldiameter of rod 32 is slightly less than the internal diameter of thesleeve 33, and then positioned securely by set screw 34, or otherappropriate means.

An upper guide arm brace 35 and a lower guide arm brace 36 are eachbolted by a flattened end to a lug 37 positioned on the trailing side ofguide arm 26. These arms diverge from that point, arm 36 being bolted bya flattened end to the frame 22 at lug 38 and arm 35 being bolted to theimpeller housing 39 by having its flattened end seated on an extendinglug and bolted thereto. The upper and lower guide arms thus assume theposition shown in FIGURES 1 and 7.

The torque arm assembly, generally designated 14, is shown best inFIGURES 1, 8 and 9. The assembly comprises an elongated 'tibular memberor bar 40 having an extension such that it extends through the silo wall10. As stated previously, silos, although designed to be substantiallycircular, are usually out-of-round. In addition, the unloader isdesigned, as stated in Van Dusen Patent 2,719,058 to have a collectorarm extension which is greater than the radius of the silo, so that thecenter of the unloader orbits about the center of the silo. Hence, rod40 must be of such an extension as to accommodate the axialreciprocation of the unloader with respect to silo wall 10. Rod 40 isflattened at end 41 as perhaps best shown in FIGURE 8, and has welded orotherwise secured thereto, a bar 42 which in cooperation with rod 40forms a T. Bar 42 extends on either side of flattened end 40 as shown inFIGURE 8. One end 42A passes through sleeve 43 and is maintained inposition by a cotter key 42C for pivotal movement about a horizontalaxis therein. The other end 42B of bar 42 engages a bearing plate 44depending from angle member 45 of a supporting tripod 45-47. Since thecollecting arm 16 moves in the direction of the arrow D within the silo,it will be appreciated that the rod 40 will assume the position ofFIGURE 1, that is, adjacent the edge of the silo aperture, which is inthe direction of travel of arm 16, or what may be called the leadingedge of the aperture. In this position, end 42B will bear against plate44 to maintain the supporting triangle 45-47 in the position shown andto preclude rotation of it, the suspension and support ring 18 and chute15.

Members 45, 46 and 47 form the arms of the supporting triangle and areof angular vertical cross section as shown in FIGURE 9. Their endsterminate and are welded to three plates 45A, 46A and 47A. Plates 46Aand 47A are identical. Plate 45A has welded thereto the sleeve 43,previously described. Each of the plates 45A- 47A is apertured toreceive a stiff rod 48 which is threaded at its lower end 49 andprovided with a plurality of nuts 50. At its upper end 51, it is turnedto receive a loop of S hook 52, the other loop of which is secured tothe silo unloader suspension cable 53 which is used for elevation of thesilo unloader when necessary as well as to provide partial support asdescribed in Patent 2,719,058.

The nuts 50 will be adjusted upwardly or downwardly on the threaded endof rod 48 to vary the effective length of the rod, both for accuratelevelling of the silo unloader initially and to lower or elevate thesupport triangle 46-47 at any corner to determine the pressure that willbe brought by the collector arm on the ensilage at a particular place asit travels its circular path within the silo so as to meet any unusualcondition within the silo such as hard material in a particular place orthe like.

The use of stiff, substantially inflexible rods 48 instead of flexiblecables insures that if the collector arm 16 should drop at anyparticular time, as due to a soft spot in the ensilage or the like,tension will be exerted on the adjacent rod or rods 48 and the silounloader will tend to pivot about a horizontal axis forcing the rod orrods on the opposite side of the collector arm to elevate, thus movinghook 52 over center and toward the silo wall in the direction of the sodropping collector arm. Such similar levelling action results if thecollector arm should elevate at a hard spot. Such action will meet asubstantial resistance due to the weight of the unloader on the cable 53and thus there is provided a further levelling action by use of thethree adjusting rods 48, instead of flexible cables.

The triangle 45-47 is bolted or otherwise suitably secured to thecollector ring assembly 18 which serves not only as a suspension andsupport ring assembly but to transfer electricity from an appropriatesource of power to the motor 20. Such structure is shown generally inPatent 2,794,560 and the specific ring used is shown in co-pendingapplication Serial No. 814,915. Reference is made to these for a morecomplete explanation of the ring assembly, although since it forms nopart of the invention per se, it is not explained in greater detail.

Secured to the top of the ring 18 is a chute generally designated 15 ofthe type shown in Patent 2,877,907, supported by a rod 54 from a sleevepivoted on a stud attached to torque arm 40, rod 54 having an upperturned end position in a second suitable sleeve secured to chute 15.

The collector arm assembly of this invention comprises the frame members30 and 31, previously described, extending the full length of theunloader as shown in FIGURE 1. These frame members are appropriatelybraced at suitable intervals. Bolted or otherwise secured by lugsthereto to depend therefrom and be supported thereby, is a gear boxassembly 19, which supports one end of each of the shafts 55 and 56 forthe collector arm augers SSA-B and 55C-D. The other ends of shafts 55and 56 are journalled in suitable bearings in depending members 57 and58 of outboard frame support 59 and each having a wall cleaner 59Asecured thereto as shown in Patent 2,719,058, which need not beexplained in further detail here.

The outboard frame support 59 has a flat horizontal plate portion 60joined to and extending between frame members 30 and 31. Plate portion60 is bolted to a pair of flat strap members 61 in turn welded tomembers 30 and 31.

Guide wheels 62 and 63 are journalled on plate 60 for rotation about avertical axis, and for engagement with the interior surface of the silowall 10 for guiding the unloader in its travel within the silo and forpositioning wall cleaners 59A with respect to the silo wall as shown inFIGURE 6. A T-bar 64 extends between plate 60 and cross brace 65. Brace65, as shown in FIGURE 2, extends between members 30 and 31 and isbolted to lugs upstanding therefrom. T-bar 64 is secured by a foot 66bolted or otherwise affixed to plate 60 and by a second inturned foot66A bolted or otherwise secured to cross brace 65. Positioned on theT-bar 64 as shown best in FIGURE 4 is a weight 67 having a set screw 68for positioning it after it has been adjusted by sliding it inwardly oroutwardly on bar 64 (rightwardly or leftwardly with reference to FIGURE2). Thus, the weight 67 serves as an adjustable means for controllingthe pressure which the outward end of the collector arm engages on theensilage.

Two top shield members 70 and 71 are positioned to extend from overlyingengagement with one of the flanges of inverted T-bar member 64downwardly and around their respective frame members 31 and 30. Asshown, there are positioned on members 30 and 31 by having an edgecurled thereabout and are secured to,

the T-bar by bolts 72.' Thus, in removal or insertion the curled edge 73would be positioned about its respective.

frame member and the opposite edge 74 positioned over the T-bar flangeand bolts 72 inserted to retain the top shield portions 70 and 71 inposition. However, if desired, rolled edges 73 may be otherwise securedto there respective frame members 30 or31.

The front top shield 75 is provided of the configuration shown (FIGURE2) and extends between members 29 and 65, being bolted to these membersby downwardly turned ends. It closes the top of the unloader between theimpeller housing 39, the frame member 30, and members 29 and 65.

A guard rod 76 extends between brace 36 and the outboard end of a framemember 30, as shown in FIGURE 2. It is provided with flattened endssecured to lugs on these respective members.

The drive hub assembly 17 is provided with a tie bar 80, as shown inFIGURE 1, through which driving force is imparted to the unloader. It isalso provided with a drive shaft 81 which serves to rotate the hub andwhich receives power from gear box assembly 19.

Frame extensions 82 and 83 are adjustably secured to frame members 30and 31 (by set screws or the like, not shown) and support acounterweight 84 on a cross bar 85 extending therebetween. The motor ismounted on a platform 86, supported on frame members and 31 as shown inFIGURE 1. Through belt drives, as shown, the motor 20 drives the gearmechanism in housing 19 from which the auger shafts 55 and 56 are drivenand from which the drive shaft 81 is driven. In such fashion motor 20also drives the shaft 87 for the central impeller in housing 39.

As is shown in FIGURE 3, the auger flighting 55A is a righthandflighting when viewed in the direction of the arrow 88, in whichdirection material is conveyed as the shaft 55 rotates in the directionof the arrow 89. A reverse half flight section 55B is positioned insubstantially continuous extension with flight section 55A.

and in the relation shown with reference ,to the front entrance 112 ofimpeller housing 39 as shown in FIG- URE 5. This reverse flighting 55Bblocks further travel of material in the direction of the arrow 88adjacent the entrance to the impeller housing so that such material willbe conveyed into the impeller at end 112.

The flighting 55C, when viewed in the direction of the arrow 88 is alefthand flighting and serves to convey material in the direction of thearrow 88 as the shaft 56 rotates in the direction of the arrow 92. Aflat straplike extension 93 is provided at the inboard end of flighting55C, and at an axial position with reference to shaft 56 slightly to theoutboard side of the intersecting prolongation of the axis of shaft 87.

Positioned on the opposite side of shaft 56 is a second straplikeextension 93A which forms a continuation of the reverse flighting 55Dwhich flighting conveys material in the direction of the arrow 94.

The particular cooperation of the forward and reverse flighting of theaugers of the collecting arm, and the cooperation of the straplikemembers 93 and 93A with impeller housing 39 provides that material willbe gathered and brought inwardly by the double angers, precluded fromcontinuing along the rear of the impeller housing by flighting 55B, andbrought into the impeller housing at front entrance and through its sideentrance 95, flighting 55C serving to bring it inwardly to force it inat 90 and 95, straps 93 and 93A serving additionally to direct materialinwardly in a direction axial to impeller shaft 87. Flighting 55Dcollects material and brings it into communication with blades or straps93 and 93A to force a stream of material inwardly in a 6 direction axialwith shaft 87. Thus, it will be seen that material will enter theimpeller housing at entrance 112 and entrance 95 by being urged in thatdirection through such cooperation.

Welded or otherwise secured to the bottom of frame member 31 by itsinturned end 98 is a collector shield 99 which extends the length ofauger flighting SSA-B. An end shield 100 is bolted by turned edges101-102 to shield 99 and to a flange 103 of housing 39. Flange 103 has acut-out portion to accommodate shaft 55 as shown in FIGURE 7.

The central impeller housing 39 comprises a front wrap 106 whichterminates at 106A as shown. It also includes a rear wrap 107terminating at edge 108 which with side plates 109 and 110 form a scrollhousing having an outlet 111, a front entrance at 112, and a sideentrance at 95. Rear wrap 107 is provided with a strap or.plate member113 having one edge flush with edge 108 and positioned therebeneath. Ithas upturned ends 113Awhich are positioned on plates 109 and 110respectively and welded or otherwise secured thereto. Thus, member 113serves to reinforce edge 108 and to provide a cutting edge, or dividingedge for the conveyed stream of material. Welded to the wrap 107 behindmember 113 is a stop bar 114 extending thereacross which serves tocollect ensilage which would otherwise pass therebeyond and retain itfor accumulation and entrance into the impeller housing 39.

Each of the plates 109 and 110 flare outwardly adjacent edge- 106A ofwrap 106 to form outwardly extending triangular portions 115 as shown inFIGURE 4. While the rear plate 110 has a bottom edge which extendssubstantially circularly to its junction with portion 103 front plate109 has a bottom portion removed to edge 116 in a vertical direction andto inclined edge 117 to form an obtuse angle cut-out as shown in FIGURE5. This is the cut-out forming the side entrance previously designated95.

Starting at 'portion 117 the rear wrap 107 is progressively rounded andfront rear plates 109 and 110 bevelled so that they terminate at edge118, to which the edges of wrap 107 are joined so that the exit 111 ofthe housing 39 assumes the rounded configuration shown in FIG- URE 2.

The central impeller. 39A comprises a central impeller disc 120 of theconfiguration shown best in FIGURE 5. It is keyed to shaft- 87 and isformed from a circular segment with arcuate portions removed so that itassumes the configuration of a triangle with rounded corners as shown inFIGURE 5. It is provided with a peripheral strengthening flange 121 andradial strengthening flanges 122. It is also provided with a pluralityof bosses 123 apertured to receive the pins 124 secured in position bycotter keys 125 and serving with washers 126 to retain the paddles 127thereon. A plurality of three paddles is provided, each of theconfiguration shown and described in US. Patent No. 2,958,412.

Guide wheels 62 and 63 may be adjusted longitudinally of the collectorarm. The structure for accomplishing this adjustment is shown anddescribed in relation to wheel 62 only. It consists of an axle boltwhich extends upwardly through a slot 151 in plate 60. The head 152 ofthe axle bolt 150 is below the plate. A jam nut 153 cooperates with head152 to clamp axle bolt 150 in any desired position in the slot 151.Guide wheel 62 is held on the axle bolt rotatably by means of the washer154 and the hub nut 155. When it is desired to adjust the longitudinalposition of axle bolt 150, the hub nut 155 is removed which makes itpossible to remove the guide wheel 62. Wrenches may then be appliedconveniently to head 152 and jam nut 153 so that the latter can beloosened. Bolt 150 may then be longitudinally slid in slot 151 to thedesired position and the jam nut 153 retightened. After this adjustmentis made, the guide wheel may then be replaced and washer 154 and hub nut7 155 returned to hold the guide wheel rotatably on the axle bolt 150.

Comparable structure secures guide wheel 63 to plate 60, the end of anaxle bolt 156 and the hub nut 157 appearing in plan view, FIGURE 2.

From the foregoing it will be seen that there are provided certain newand useful improvements in silo unload-ers designed to accomplish theforegoing objects of this invention.

It is apparent that many modifications and variations of this inventionas hereinbefore set forth may be made without departing from the spiritand scope thereof. The specific embodiments described are given by wayof example only and the invention is limited only by the terms of theappended claims.

What is claimed is:

1. In a silo unloader collector arm, a rotary auger assembly, elongatedcenter beam means positioned above and extended longitudinally of saidauger assembly, elongated frame members positioned on opposite sides ofthe center beam means and extended substantially parallel thereto,shield means for covering said auger assembly, said shield meansincluding a first sheet member projected outwardly from the center beammeans and a second sheet member projected outwardly in an oppositedirection from the center beam means, each sheet member having anarcuate outer edge cooperating with an arcuate surface of the adjacentframe member, said first sheet member and second sheet member being ofsubstantially the same size and shape, and means for securing the firstsheet member and the second sheet member to the center beam means.

2. In a silo unloader an impeller housing having an upright Wall and afront wall, said upright Wall having a bottom side opening and saidfront wall having a front opening, impeller means located within saidhousing and rotatable about a generally horizontal axis to move materialthrough s'aid' housing, an elongated material collector means for movingmaterial toward said housing and through said openings, said collectormeans including a member positioned adjacent the outside of said uprightwall operable to move material through the side opening into thehousing, elongated frame means positioned on opposite sides of thehousing and extended substantially parallel to the material collectormeans, an elongated center beam means positioned above and extendedsubstantially parallel to said collector means, shield means forcovering said collector means, said shield means including a first sheetmember projected outwardly from the center beam means and a second sheetmember projected outwardly in an opposite direction from the center beammeans, means for securing both sheet members to the center beams, theouter edges of the sheet members engageable with adjacent frame members,top shield means extended laterally and outwardly from said upright wallabove the member operable to move material through the side opening, andthird shield means secured to and projected downwardly from one of theframe members for guiding material toward said front opening in thehousing.

3. The structure of claim 2 including plate means secured to outer endsections of the frame members, and guide wheel means rotatably mountedon said plate means for maintaining a spaced relation between the outerend of the material collector means and the Wall of a silo.

4. The structure of claim 2 wherein said collector means comprises apair of spaced elongated angers, one of said augers having a sectionlocated adjacent the outside of said vertical upright wall for movingmaterial into the housing through the bottom side opening.

5. The structure of claim 2 wherein the outer edges of the sheet membershave arcuate edges cooperating with arcuate surfaces on adjacent framemembers.

6. The structure defined in claim 3 wherein said plate means has a slottherein extending in the direction of desired adjust'ability, a threadedaxle member extending upward through the slot of said plate means withits head beneath it, a first nut on said axle member and on top of saidplate means, said first nut cooperating with the head of said threadedaxle member to clamp said axle member to said plate means, a guide wheelrotatably embracing said axle member on top of said first nut, andsecond removable nut means for securing said guide wheel on said axle.

References Cited by the Examiner UNITED STATES PATENTS 2,671,696 3/1954McLean.

2,711,814 6/1955 McCarthy.

2,864,655 12/1958 Caron.

2,921,670 1/1960 Albers l98213 2,995,260 8/1961 McCann et al 214-173,079,016 2/1963 Dretzke 214-17 GERALD M. FORLENZA, Primary Examiner.

ROBERT G. SH'ERDIAN, Examiner.

1. IN A SILO UNLOADER COLLECTOR ARM, A ROTARY AUGER ASSEMBLY, ELONGATEDCENTER BEAM MEANS POSITIONED ABOVE AND EXTENDED LONGITUDINALLY OF SAIDAUGER ASSEMBLY, ELONGATED FRAME MEMBERS POSITIONED ON OPPOSITE SIDES OFTHE CENTER BEAM MEANS AND EXTENDED SUBSTANTIALLY PARALLEL THERETO,SHIELD MEANS FOR COVERING SAID AUGER ASSEMBLY, SAID SHIELD MEANSINCLUDING A FIRST SHEET MEMBER PROJECTED OUTWARDLY FROM THE CENTER BEAMMEANS AND A SECOND SHEET MEMBER PROJECTED OUTWARDLY IN AN OPPOSITEDIRECTION FROM THE CENTER BEAM MEANS, EACH SHEET MEMBER HAVING ANARCUATE OUTER EDGE COOPERATING WITH AN ARCUATE SURFACE OF THE ADJACENTFRAME MEMBER, SAID FIRST SHEET MEMBER AND SECOND SHEET MEMBER BEING OFSUBSTANTIALLY THE SAME SIZE AND SHAPE, AND MEANS FOR SECURING THE FIRSTSHEET MEMBER AND THE SECOND SHEET MEMBER TO THE CENTER BEAM MEANS.